Not related to your question as such but your joomla version is WAY out of date. (3.6.4 vs new version 3.7.5).

I would suggest using Googles Page Speed tools and follow the recommendation it offers following the tests. You were pretty much spot on with the "12 seconds" because Page speed's test showed it took 12.5 seconds to load......

have you updated all extensions in your site to the latest versions? I think you should really check if you need all these plugins, modules, components etc and try to slim down your installed extensions you have there that is not necessary.

I also see that the template Helix 3 version shows 1.7 and the latest version i 2.2 if thats correct.. "Templates :: SITE :: shaper_helix3 (1.7)"

Cheers!

Success in the long run Its not about the code its about the people and community that's make it!Its not what you say its what you do that matters!